The present invention relates to a drive system for tranporting a work member over a predetermined path.
The situation often arises that due to limitations upon the available work space, the size of the mast structure holding a work member, such as a drill, can be severely limited. Such a situation can especially occur, for example, when working inside a tunnel, such as in subway construction. Additionally, for purposes of transportation, it becomes desirable to limit the size of the mast in order that the system is more easily transportable. While the desirability of condensing the size of the mast structure exists with all types of drive systems, it becomes especially significant in the utilization of hydraulic drive systems.
In the utilization of a single end hydraulic cylinder, the path of travel for the work member is basically equal to the active length of the cylinder. The overall length of the structural mast which is required however, is essentially equal to the distance of travel plus the length of the piston. While the utilization of such a single end cylinder provides for a relatively compact system, it has several drawbacks. One such drawback is that the effective force which can be supplied is significantly reduced on the rod end by the area of the rod itself. Additionally, when activating the piston end, the rod is placed in compression and for structural reasons this tends to limit the total practical length of the system.
It is alternatively possible to utilize a double end cylinder which eliminates the drawbacks associated with the use of a single end cylinder. In utilizing such a double end cylinder, however, the total length of the assembly has to be equal to two times the total path in addition to the length of the two end caps of the piston. Consequently, the utilization of such a system significantly increases the size of the necessary mast structure.
Accordingly, with any of the previously known systems, it is necessary that in order to transport a work member over a predetermined path that a certain minimal dimension in relation to the corresponding dimension of the path be utilized. In the use of a double end cylinder, as noted above, this minimal dimension is approximately two times the distance of the predetermined path. In the utilization of other drive systems however, the minimal dimension dimension would be substantially equal to the length of the predetermined path.